1. Field of the Invention
The invention relates to the field of automated inspection equipment, and in particular concerns video based inspection equipment integrated with the manufacture of blow molded containers, especially containers of polyethylene terephthalate (PET), PEN or similar materials. The inspection system is fit into and synchronized with a multiple-station production machine, such that selections can be correlated to particular forming and conveying apparatus, and there is no interference by the inspection system with handling of the containers through production.
2. Prior Art
Automated optical inspection systems for containers such as beverage bottles are known and can be applied to the detection of defects in newly manufactured containers or used containers, e.g., containers that are recycled after being returned for deposit. Recycled bottles are cleaned and inspected for dirt or damage prior to refilling. U.S. Pat. No. 4,459,023-Reich et al. is an example of an inspection system for returnable bottles.
Returnable bottles are typically made of glass, whereas recycled plastic bottles are more likely to be comminuted and used as a source of plastic for other uses. Examples of defects that may render a returned glass bottle unusable are chips or cracks, especially associated with the surface to be sealed against a closure cap, cracks, dirt and extensive scuffing of the exterior surface.
Newly manufactured bottles are less likely to have comparable defects because they have not yet suffered rough handling during distribution or consumer use. However, new containers also can be inspected for defects that may arise due to the manufacturing process used to make them. One such process involves the blow-molding of polyethylene terephthalate containers, which are in use for beverage containers and the like.
In a typical inspection system, for example for returnable bottles, the inspection system treats each bottle independently of all other bottles. Bottles which are rejected are diverted from the serial stream of bottles, typically by a reject mechanism located some distance downstream from the inspection system along a conveying means. This requires a shift register or other synchronizing means causing the downstream diverter to operate on the correct bottle when it arrives. Since there is no relationship between the bottles being conveyed and inspected, data from the inspection system can only be used to develop statistical information respecting the overall population of bottles.
In a production setting, information collected at inspection stations and other quality assurance steps is advantageously correlated to the particular materials, apparatus and the like that were used to produce the product being checked. Process engineers therefore may attempt to cross-correlate selections rates with the content of specific batches of material, process parameters such as temperatures and pressures measured during production, etc., in order to adjust the process parameters so as to maximize selections.
According to the present invention, an inspection system is integrated with and synchronized to a multiple station production machine wherein each of the stations is used repetitively in turn. As a result, it is possible separately to analyze the performance of each station. Unlike container inspection systems that treat each container independently, the system of the invention is useful for correlating selection information to elements of the production machine. This is especially useful in the blow molding of PET/PEN bottles.
PET/PEN material is durable and light in weight. The manufacturing process typically involves preliminary molding of the closure end of the container, retaining a preform that is then heated to softening and blow molded to form the container body. The container body can have a flat bottom that may be covered by a plastic cup for protecting the bottom and making the empty container bottom-heavy. According to another technique, the bottom of the container is formed into folds that define lobes for strengthening the bottom. An example is the so-called "petaloid" bottom configuration, having several lobes formed by folds in the bottom of the container during the molding process.
Whether used for new containers or containers returned for re-use, the typical bottle inspection system is a stand-alone unit mounted along a conveyor. The containers successively pass through an inspection station where optical apparatus record one or more images of the container by one means or another, and analyze the data for defects. Such defects typically are detected from unexpected variation in the reflectance level of the bottle or its light transmission characteristics, wherein a local variation in reflectance or transmissiveness may be due to a crack, chip or molding fault.
An example of such a stand alone bottle inspection system may be seen in U.S. Pat. No. 3,932,042-Faani et al., which discloses an inspection system which utilizes a conveyor to transport a line of newly manufactured bottles through an inspection station. The inspection station performs various optical tests on each of the bottles in the line. The inspection system triggers a deflection mechanism or kicker downstream along the conveyor, and either accepts or rejects each bottle based on the test results. The reject signal can operate a solenoid, air cylinder or the like to remove or divert a rejected bottle.
The optical tests used to detect defects can be complicated or simple, and various optical inspection techniques can be used to resolve the different defects that can occur. A simple test could involve, for example, checking only for a correctly shaped sealing surface on the end of the bottle, or only for gross defects in the external contour. While these are useful tests, it would be advantageous to provide a sequence of tests for a variety of potential defects. Thus the sidewalls of the bottle can be examined, neck threads can be checked for continuity, the endmost sealing surface can be checked for smoothness and the bottom lobes can be checked for complete formation during molding.
It has been found according to the present invention that certain defects caused by physical obstructions in particular mold cavities or blow molding conduits can persist through successive uses of the cavities or the like. As a result, in a multiple station apparatus having N stations, every Nth container may have a similar defect. Similarly, a temperature or pressure problem at a given mold cavity may not cause a defect with every use, but may simply be statistically more likely to cause a defect. Furthermore, certain kinds of different defects can be related to the same deficiency of the molding apparatus. Using a digital processor in sync with the molding equipment according to the invention, it is possible to identify problems more quickly and to use the synchronous relationship of the inspection and molding steps to isolate the exact cause of molding problems. The same is true of problems in handling equipment synchronized to the molder, such as damaged grasping apparatus.
In Faani et al., an inspection system illuminates each bottle from two different directions as the bottle is transported along a conveyor. The light passes through or is reflected by various portions of the container and is directed through a mirror arrangement and resolved to form an image. The image is presented to a single scanning device such that the scanning device attempts to glean enough information to accept or reject the bottle without its having to be rotated for presentation of all the sides.
U.S. Pat. No. 3,880,750-Butler et al. discloses an inspection system for inspection of the sealing surface of the bottle, namely the endmost surface that forms a sealing closure together with a cap. A light source is positioned above the rim of the bottle and directs an intense spot light of light onto the rim. A detector is positioned above the rim of the bottle such that light reflected from the rim is passed through a mask to a detector. The bottle under inspection is rotated about its vertical axis during the inspection cycle, and variations in the detected light level are detected when caused by scattering of the light beam by a defect. The electronic signal produced by the detector can be processed through circuitry allowing the system to detect several types of defects in the shape or character of the sealing surface.
The foregoing inspection systems are ancillary to the container production steps because the inspection system can be placed at any point where there is a stream of containers moving along a conveyor and synchronism of the inspection and production are not required. This is advantageous for an inspection system because the inspection system needs a clear view of the containers, free of obstruction by handling equipment, conveyor rails and other structures that could conceal a defect. The inspection station can have distinct handling apparatus specifically adapted for inspection steps. For example, the handling apparatus may be designed to engage and rotate each bottle during the inspection cycle to ensure that each sidewall is presented for inspection. On the other hand, the mechanism associated with an inspection step such as rotating the bottle, may be inconsistent with another step, such as examining the sealing surface or threads. Therefore, a comprehensive inspection system tends to be relatively complex.
It would be desirable to integrate an inspection system with container manufacturing equipment, so as to eliminate the need for additional handling equipment such as conveyers and other dedicated equipment. The present invention is intended to integrate inspection steps with manufacturing steps, especially in the blow molding of polyethylene terephthalate beverage containers and the like, for identifying and segregating defective containers as early as possible during their production and handling, and by inspecting the containers when the manufacturing equipment happens to orient the containers appropriately for certain inspection steps. Moreover, by integrating the inspection system closely with the container production equipment (e.g., the molder) and the feeding and take-out apparatus that are synchronous with the production equipment already, the foregoing capability of correlating selection results and even specific types of defects, to the particular station that produced each container, is greatly enhanced.